1. Field of the Invention
The present invention relates to an alternator driven by an internal combustion engine, for example, and relates to an automotive alternator mounted to an automotive vehicle such as a passenger car or a truck, for example.
2. Description of the Related Art
FIG. 12 is a cross section of a conventional automotive alternator, and FIG. 13 is a perspective of a rotor 107 in FIG. 12.
This alternator is provided with: a case 3 constituted by a front bracket 1 and a rear bracket 2 made of aluminum; a shaft 6 disposed inside the case 3, a pulley 4 being secured to a first end portion of the shaft 6; a Lundell-type rotor 107 secured to the shaft 6; fans 105a and 105b secured to first and second end surfaces of the rotor 107; a stator 108 secured to an inner wall surface inside the case 3; slip rings 9 secured to a second end of the shaft 6 for supplying electric current to the rotor 107; a pair of brushes 10 sliding on surfaces of the slip rings 9; a brush holder 11 for accommodating the brushes 10; a rectifier 12 electrically connected to the stator 108 for converting alternating current generated in the stator 108 into direct current; and a regulator 18 fitted onto the brush holder 11, the regulator 18 adjusting the magnitude of the alternating voltage generated in the stator 108.
The rotor 107 is provided with: a rotor coil 13 for generating magnetic flux on passage of an electric current; and a pole core 14 disposed so as to cover the rotor coil 13, magnetic poles being formed in the pole core 14 by the magnetic flux from the rotor coil 13. The pole core 14 is constituted by a first pole core portion 121 and a second pole core portion 122 which are alternately intermeshed with each other. The first pole core portion 121 and the second pole core portion 122 are made of iron, and are constituted by: first and second disk portions 201 and 202 which are surfaces perpendicular to an axis; first and second claw-shaped magnetic poles 123 and 124 having a tapered shape extending axially from the disk portions 201 and 202 so as to face each other; and a cylindrical portion 200 connecting the disk portions 201 and 202 to each other, a circumference of the cylindrical portion 200 being covered by the rotor coil 13.
As shown in FIGS. 14 and 15, on side surfaces of the claw-shaped magnetic poles 123 and 124 each constituting a facing surface between adjacent first and second claw-shaped magnetic poles 123 and 124, values of xcex1 and values of xcex2 are equivalent, where xcex1 is an angle formed between the side surface at a tip 123A of a claw-shaped magnetic pole 123 or 124 and a radial line of the claw-shaped magnetic pole 123 or 124, and xcex2 is an angle formed between the side surface at a root portion 123B of a claw-shaped magnetic poles 123 or 124 and the radial line.
FIG. 16 is a perspective of the stator 108 in FIG. 12, FIG. 17 is a perspective of a stator core 115 in FIG. 12, and FIG. 18 is a partial plan of the stator core 115 in FIG. 17.
The stator 108 is constituted by: a stator core 115 formed by laminating a plurality of steel sheets for passage of a rotating magnetic field from the rotor coil 13; and a three-phase stator winding 116 through which an output current flows. The stator core 115 is constituted by: an annular core back 82; and a plurality of teeth 81 extending radially inward from the core back 82 at a uniform pitch in a circumferential direction. The three-phase stator winding 116 is housed in a total of thirty-six slots 83 formed between adjacent teeth 81. The teeth 81 are constituted by: tip portions 85 projecting in a circumferential direction of the stator 108; and stanchion portions 86 connecting the tip portions 85 and the core back 82. Gaps called opening portions 84 are formed between the tip portions 85 of adjacent teeth 81.
Moreover, this example is a three-phase alternator in which the total number of slots 83 is thirty-six and the total number of claw-shaped magnetic poles 123 and 124 is twelve, the slots 83 being formed at a ratio of one per phase per pole.
In the automotive alternator of the above construction, an electric current is supplied from a battery (not shown) through the brushes 10 and the slip rings 9 to the rotor coil 13, generating a magnetic flux and giving rise to a magnetic field. At the same time, since the pulley 4 is driven by the engine and the rotor 107 is rotated by the shaft 6, a rotating magnetic field is applied to the stator core 115, generating electromotive force in the stator winding 116 and an output current is generated by an external load connected to the automotive alternator.
Now, the magnetic flux A generated by the rotor coil 13 leaves the first pole core portion 121, which is magnetized with north-seeking (N) poles, crosses an air gap between the rotor 107 and the stator 108, and enters the teeth 81 of the stator core 115. This magnetic flux A then passes through the core back 82, and flows from adjacent teeth across the air gap to the second pole core portion 122, which is magnetized with south-seeking (S) poles.
The amount of magnetic flux, which determines the output of the alternator, is itself determined by the magnetomotive force of the rotating magnetic field from the rotor 107 and magnetic resistance of the above magnetic circuit followed by the magnetic flux A. Consequently, if the magnetomotive force is constant, then it is important to shape this magnetic circuit so as to have minimal resistance.
Furthermore, in order to improve the magnetomotive force, it is necessary to increase AT (the field current I multiplied by the number of turns n of conductor wires in the rotor coil 13), but AT is determined by installation space for the rotor coil 13 inside the pole core 114. When the overall size of the rotor 107 is limited, it becomes necessary to reduce the cross-sectional area of the magnetic path through the pole core 114 in exchange for increases in installation space for the rotor coil 13, and as a result the above-mentioned magnetic resistance increases, reducing the amount of magnetic flux passing through the pole core 114 and preventing the magnetomotive force from increasing.
If attempts are made to increase the magnetomotive force by increasing the field current I while keeping the cross-sectional area s of the conductor wires and the number of turns n constant, the temperature of the rotor coil 13 increases due to copper loss in the rotor coil 13, and the resistance of the conductor wires in the rotor coil 13 rises due to the increase in temperature, reducing the field current I and preventing the magnetomotive force from increasing after all.
On the other hand, as shown in FIG. 19, Japanese Patent Laid-Open No. HEI 11-164499 discloses an alternator aimed at increasing magnetomotive force by setting a ratio L1/L2 between an axial length L1 of the stator core 115 and an axial length L2 of the cylindrical portion 200 within a range of 1.25 to 1.75, placing the disk portions 201 and 202 opposite the stator core 115 so that the magnetic flux A flows directly from the disk portions 201 and 202 into the stator core 115, thereby increasing the cross-sectional area of the magnetic path through the pole core 114, and setting a ratio between an outside radius R1 of the claw-shaped magnetic poles 123 and 124 and an outside radius R2 of the cylindrical portion 200 between 0.54 and 0.60, thereby increasing the cross-sectional area of the magnetic path through the cylindrical portion 200.
However, in the automotive alternator according to the above Patent Laid-Open, no consideration at all has been given to the dimensions, shapes, etc., of the claw-shaped magnetic poles 123 and 124, and for example, when the ratio between the radial thickness of the tips 123A of the claw-shaped magnetic poles 123 and 124 and the radial thickness t2 of the root portions of the claw-shaped magnetic poles 123 and 124 is large, in other words, when the thickness of the tips of the claw-shaped magnetic poles 123 and 124 is large, one problem has been that the surface area of the side surfaces of the claw-shaped magnetic poles 123 and 124 which face each other is large even at the tips of the claw-shaped magnetic poles 123 and 124 and the amount of xe2x80x9cmagnetic flux leakagexe2x80x9d increases, that is, a large portion of the magnetic flux flows from those side surfaces to the side surfaces of adjacent claw-shaped magnetic poles 124, reducing effective magnetic flux, and thereby leading to reduced output current.
When the size of the entire rotor 107 is limited, another problem has been that there are constraints on winding a large number of conductor wires with respect to installation space for the rotor coil 13, making the output current low.
The present invention aims to solve the above problems and an object of the present invention is to provide an alternator in which output current is improved by increasing effective magnetic flux.
In order to achieve the above object, according to one aspect of the present invention, there is provided an alternator wherein: a ratio (t1/t2) between a radial thickness (t1) of a tip of claw-shaped magnetic poles and a radial thickness (t2) of a root portion of the claw-shaped magnetic poles is within a range equal to or greater than 0.10 and equal to or less than 0.25 (0.10xe2x89xa6t1/t2xe2x89xa60.25), and
a ratio (A/B) between a dimension (A) of overlap between a stator core and disk portions when viewed from a radial direction and an axial dimension (B) of the disk portions is within a range equal to or greater than 0.2 and equal to or less than 1.0 (0.2xe2x89xa6A/Bxe2x89xa61.0).
According to another aspect of the present invention, there is provided an alternator wherein:
a ratio (Lp/Lc) between an axial length (Lp) of claw-shaped magnetic poles overlapping the stator core when viewed from a radial direction and an axial length (Lc) of the stator core is within a range equal to or greater than 0.7 and equal to or less than 0.9 (0.7xe2x89xa6Lp/Lcxe2x89xa60.9).